The overall objective of this study is to develop a more coherent understanding of the etiology and pathophysiology of the age-related bone loss that leads to osteoporosis. We initially reported in an abstract that compared to normal postmenopausal women, women with postmenopausal osteoporosis have decreased tubular reabsorption of calcium and sustained renal calcium wasting. It was independent of PTH action and concluded that a primary defect in renal calcium conservation may be a major cause of the negative calcium balance in postmenopausal osteoporosis. We have since expanded this project to include normal and osteoporotic postmenopausal women on estrogen to test if estrogen corrects the defect in renal calcium conservation in women with osteoporosis. We are in the process of analyzing those samples. A further extension of this study is explored in our protocol, 802-95.